1. Field of the Invention
Embodiments disclosed herein relate generally to irregular pressure vessels used in the oil and gas industry. Specifically, embodiments disclosed herein relate to a method of manufacturing or reinforcing blowout preventers.
2. Background
Well control is an important aspect of oil and gas exploration. When drilling a well, for example, safety devices must be put in place to prevent injury to personnel and damage to equipment resulting from unexpected events associated with the drilling activities.
The process of drilling wells involves penetrating a variety of subsurface geologic structures, or “layers.” Occasionally, a wellbore will penetrate a layer having a formation pressure substantially higher than the pressure maintained in the wellbore. When this occurs, the well is said to have “taken a kick.” The pressure increase associated with the kick is generally produced by an influx of formation fluids (which may be a liquid, a gas, or a combination thereof) into the wellbore. The relatively high pressure kick tends to propagate from a point of entry in the wellbore uphole (from a high pressure region to a low pressure region). If the kick is allowed to reach the surface, drilling fluid, well tools, and other drilling structures may be blown out of the wellbore. Such “blowouts” may result in catastrophic destruction of the drilling equipment (including, for example, the drilling rig) and substantially injure or result in the death of rig personnel.
Because of the risk of blowouts, devices known as blowout preventers are installed above the wellhead at the surface or on the sea floor in deep water drilling arrangements to effectively seal a wellbore until active measures can be taken to control the kick. Blowout preventers may be activated so that kicks are adequately controlled and “circulated out” of the system. There are several types of blowout preventers, the most common of which are ram blowout preventers and annular blowout preventers (including spherical blowout preventers).
Annular blowout preventers typically use large, annular, rubber or elastomeric seals having metal inserts, which are referred to as “packing units.” The packing units may be activated within a blowout preventer to encapsulate drill pipe and well tools to completely seal an “annulus” between the pipe or tool and a wellbore. In situations where no drill pipe or well tools are present within the bore of the packing unit, the packing unit may be compressed such that its bore is entirely closed. Typically, packing units seal about a drill pipe, in which the packing unit may be quickly compressed, either manually or by machine, to result in a seal thereabout, preventing well pressure from causing a blowout. Examples of annular blowout preventers are disclosed in U.S. Pat. Nos. 2,609,836 and 5,819,013, each of which is incorporated herein by reference in their entireties. An example of a spherical blowout preventer is disclosed in U.S. Pat. No. 3,667,721, incorporated herein by reference in its entirety.
Ram blowout preventers typically have a body and at least one pair of horizontally opposed bonnets. The bonnets are generally secured to the body about their circumference with, for example, bolts. Alternatively, bonnets may be secured to the body with a hinge and bolts so that the bonnet may be rotated to the side for maintenance access. Interior of each bonnet is a piston actuated ram. The rams may be either pipe rams (which, when activated, move to engage and surround drill pipe and well tools to seal the wellbore), shear rams (which, when activated, move to engage and physically shear any drill pipe or well tools in the wellbore), or blind rams (which, when activated, seal the bore like a gate valve). The rams are typically located opposite of each other and, whether pipe rams, shear rams, or blind rams, the rams typically seal against one another proximate a center of the wellbore in order to completely seal the wellbore.
The rams are generally constructed of steel and fitted with elastomeric components on the sealing surfaces. The ram blocks are available in a variety of configurations allowing them to seal a wellbore. Pipe rams typically have a circular cutout in the middle that corresponds to the diameter of the pipe in the hole to seal the well when the pipe is in the hole; however, these pipe rams effectively seal only a limited range of pipe diameters. Variable-bore rams are designed to seal a wider range of pipe diameters. The various ram blocks may also be changed within the blowout preventers, allowing well operators to optimize the blowout preventer configuration for the particular hole section or operation in progress. Examples of ram type blowout preventers are disclosed in U.S. Pat. Nos. 6,554,247, 6,244,560, 5,897,094, 5,655,745, and 4,647,002, each of which is incorporated herein by reference in their entireties.
FIG. 1 presents a cross-section of an embodiment of a ram blowout preventer, and as described in U.S. Pat. No. 4,647,002. A blowout preventer housing body 104 may have a vertical bore 102 in which a tubular member 100 (e.g., drill pipe or oil tools) may be inserted. Housing body 104 may have one or more horizontal bores 106, 108 (two horizontal bores in a dual ram blowout preventer configuration, as illustrated). In horizontal bore 106 are ram blocks 60, shown in cross-section, each having a top seal 10 and a packing element 24. As illustrated, ram blocks 60 are in the open position. When ram blocks 60 are closed, top seal 10 acts to seal about the upper surface of horizontal bore 106 while packing element 24 inwardly seals about tubular member 100 as shown in second horizontal bore 108.
Ram blowout preventers are currently manufactured for various bore size ranges, and typically have a working pressure range from 2,000 to 15,000 psi. For example, a ram blowout preventer rated for operation at 15,000 psi may be manufactured with a base material, such as a low-alloy steel having a minimum material yield strength of 85,000 psi throughout the section thickness of the body. This minimum yield strength is necessary to prevent plastic deformation or failure of the body during both the hydro test pressure at 150% of the working pressure range (22,500 psi internal water test pressure) and during the 15,000 psi maximum internal operating pressure. The yield strength (85,000 psi) of these 15,000 psi rated ram blowout preventer bodies have been determined to be comfortably above the minimum requirements necessary for the pressure rating.
However, it may be desired to use ram blowout preventers at high pressure, high temperature conditions (above 15,000 psi and greater than 250° F.). Particularly, ram blowout preventers rated at working pressures of 20,000 psi, 25,000 psi, and higher and working temperatures of up to 350° F. or higher, may be desired. Such blowout preventers would need to meet the design criteria for metallic oil and gas field components, such as those requirements established by NACE International (formerly the National Association of Corrosion Engineers) and the European Federation of Corrosion for the performance of metals when exposed to various environmental compositions, pH, temperatures, and H2S partial pressures (including NACE MR0175, NACE TM0177, and NACE TM0284).
Alloys currently used as a base material to manufacture ram blowout preventers may not perform adequately at the higher pressures, subjecting the ram blowout preventer to plastic deformation or failure of the body. One method to produce blowout preventers with the desired high pressure rating could include manufacturing a ram blowout preventer from a higher strength base material, such as a solid high strength corrosion resistant alloy forging. However, such high strength corrosion resistant alloys are typically available only in ingots of 30,000 pounds or less, whereas approximately 100,000 pounds or more may be required to manufacture a dual cavity ram blowout preventer body. More importantly, manufacture of a blowout preventer body with such a base material may be cost prohibitive as such high-strength corrosion resistant alloys are much more expensive than low-alloy steel and are not as easily machinable as their lower strength counterparts.
Accordingly, there exists a need for high pressure, high temperature ram blowout preventers. Additionally, there exists a need for an economical means to manufacture the blowout preventers rated for operation at higher pressures and temperatures.